The key to understanding the function of the insulin receptor lies in recognizing now insulin interacts with the receptor to bring about signal transduction. Insulin receptor is a protein tyrosine kinase and protein kinases, even Ser/Thr kinases, share certain sequence homologies. If it is possible to establish that the receptor uses homologous groups to perform the same functions as these kinases, then once a 3D structure is known for these enzymes, the insulin receptor conformation can be projected onto it using the landmarks established through derivatization. The goal of the proposed research is to establish such landmarks on the insulin receptor by selective derivatization of functionally important groups and determining the site of derivatization. The first questions to be answered are 1) Where is the SH group whose alkylation inhibits receptor activation? 2) Where are the S-S bridges that bind receptor subunits together? 3) Where does insulin bind to its receptor? Answers to these questions will be sought by derivatizing with a new class of radiolabeled reagents of the general type X-R-iminobiotin where X is a derivatizing reagent, R is a spacer group, and iminobiotin is a "handle" by which the derivatized sites wi.U be isolated. These new reagents will dramatically simplify the purification of derivatized peptides. Once the location of the derivatized amino acids is established, they wi.U be replaced by point mutations of the gene for the proreceptor. Using both approaches to validate the importance of specific amino acids for receptor function and conformation will provide strong evidence that functionally important sites have been identified.